Regional climatic change following the Eocene–Oligocene Transition in central northern Tibet

The Eocene–Oligocene Transition (EOT) constitutes one of the most dramatic climatic changes in the Cenozoic era; it is characterized by global cooling, increasing aridity, extinction of fauna and flora, and a major drop of global sea level. However, how continental settings responded to global climatic change after the EOT event has still received little consideration. Here we report a high-resolution and well-dated terrestrial EOT record from the Tuotuohe Basin (central northern Tibetan Plateau). Sedimentary facies, fossil evidence, new proxy, and climate modeling data suggest a transition from warm and dry to cool and wet climatic conditions ca. 33 Ma, in contrast with other records from the Tibetan Plateau that commonly document drier conditions after the EOT (ca. 34 Ma). Having considered the potential forcing mechanisms, we propose that the Indian monsoon likely expanded into the Tuotuohe Basin after the EOT due to a combination of factors, such as the land-sea pressure gradient caused by the retreat of the Paratethys Sea, tectonic uplift in central northern Tibet and increased cross-equatorial pressure gradients. This study opens new perspectives for paleoclimate model simulations around the EOT that encompasses major environmental reorganizations at the continent scale, such as the Mongolian Re-modeling (faunal turnovers of Paleogene mammals from the Mongolian Plateau) and the Grande Coupure (extinction of a large number of European native mammals).